Method of producing a cermet-containing bushing for an implantable medical device

ABSTRACT

One aspect relates to a method for producing an electrical bushing for an implantable medical device. The method includes generating an insulation element green compact for an insulation element from an insulating composition of materials. The insulation element green compact is partially sintered. At least one cermet-containing conduction element green compact for a conduction element is formed. The at least one conduction element green compact is introduced into the insulation element green compact. The insulation element green compact and the at least one conduction element green compact are fired to obtain an insulation element with at least one conduction element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/850,406, entitled “CERMET-CONTAINING BUSHING FOR AN IMPLANTABLEMEDICAL DEVICE,” having a filing date of Aug. 4, 2010, which claimspriority to German Patent Application No. DE 10 2009 035 972.9, filed onAug. 4, 2009, which are incorporated herein by reference.

BACKGROUND

One aspect relates to an electrical bushing for an implantable medicaldevice having an annulus-like holding element for holding the electricalbushing in the implantable medical device, whereby the holding elementincludes a through-opening, at least one elongated conduction elementextends through the through-opening, and an insulation element forforming a hermetic seal between the holding element and the conductionelement is arranged in the through-opening. One aspect relates to amethod for producing an electrical bushing for an implantable medicaldevice.

DE 697 297 19 T2 describes an electrical bushing for an implantableelectrical therapeutic device. Electrical bushings of this type serve toestablish an electrical connection between a hermetically sealedinterior and an exterior of said therapeutic device. Known implantabletherapeutic devices include cardiac pacemakers or defibrillators, whichusually include a hermetically sealed metal housing, which is providedwith a connection body, also called header, on one side. Said connectionbody includes a connection socket for connecting electrode leads. Inthis context, the connection socket includes electrical contacts thatserve to electrically connect electrode leads to the control electronicsin the interior of the housing of the implantable therapeuticdevice—also called implantable device. An essential prerequisite for anelectrical bushing of this type is hermetic sealing with respect to thesurroundings.

Accordingly, it needs to be made sure that the conducting wires that areintroduced into an insulation element and via which the electricalsignals proceed, are introduced into the insulation element without anygaps. In this context, it has proven to be disadvantageous that theconducting wires in general are made of a metal and need to beintroduced into a ceramic insulation element. In order to ensurelong-lasting connection between the two elements, the internal surfaceof the bore hole in the insulation element must be metallized forsoldering the conducting wires into them. Said metallization inside thebore hole in the insulation element has proven to be difficult to apply.Homogeneous metallization of the internal surface of the bore hole inthe insulation element can be ensured only by means of expensiveprocedures.

Patent specification U.S. Pat. No. 5,769,874 describes an implantableelectrical therapeutic device. Said therapeutic device includes a sealedarea for a battery, whereby the area is provided with a coating. Saidcoating is to collect chemicals leaking from the battery. In thiscontext, the coating can be made of a cermet. For these and otherreasons there is a need for the present invention.

SUMMARY

One aspect is an electrical bushing for an implantable medical device,having an annulus-like holding element for holding the electricalbushing in the implantable medical device. The holding element includesa through-opening. At least one elongated conduction element extendsthrough the through-opening. An insulation element for forming ahermetic seal between the holding element and the conduction element isarranged in the through-opening. The at least one conduction elementincludes components made of cermet.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates an implantable medical device.

FIG. 2 illustrates a drawing of a section through an electrical bushingaccording with one embodiment.

FIG. 3 illustrates a schematic top view onto the electrical bushingaccording to FIG. 2.

FIG. 4 illustrates a detail magnification of the electrical bushing.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which isillustrated by way of illustration specific embodiments in which theinvention may be practiced. In this regard, directional terminology,such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc.,is used with reference to the orientation of the Figure(s) beingdescribed. Because components of embodiments can be positioned in anumber of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One aspect creates an electrical bushing for an implantable medicaldevice, in which the aforementioned disadvantages are avoided, and inwhich a long-lasting sealing connection between insulation element andconduction element is ensured. One aspect is an electrical bushing foran implantable medical device and one aspect is a method for producingan electrical bushing for an implantable medical device. Any featuresand details that are described in this context in relation to theelectrical bushing or the implantable medical device shall also apply inrelation to the method, and vice versa.

The electrical bushing according to one embodiment is characterized inthat the at least one insulation element includes a cermet.

According to the prior art, the conduction element is a metallic wire.In contrast, in one embodiment, the conduction element is a cermet, thatis, a composite material made of ceramic materials in a metallic matrix.A conduction element designed as described is easy to connect to theinsulation element since it is a ceramic material. Accordingly, it isfeasible to generate green compacts of both the conduction element andthe insulation element which are subsequently subjected to a sinteringprocess. The resulting electrical bushing is not only biocompatible andresistant, but also illustrates good hermetic sealing. No fissures orconnecting sites still needing to be soldered arise between theconduction element and the insulation element. Rather, sintering resultsin connection of the insulation element and the conduction element. Adevelopment of an embodiment therefore provides the at least oneconduction element to consist of a cermet. The conduction element in onedevelopment does not only includes components made of cermet, but isfully made of a cermet.

In the context of one embodiment, the terms, “cermet” or“cermet-containing”, shall refer to all composite materials made ofceramic materials in a metallic matrix (binding agent). These arecharacterized by their particularly high hardness and wear resistance.The “cermets” and/or “cermet-containing” substances are cuttingmaterials that are related to hard metals, but contain no tungstencarbide hard metal and are produced by powder metallurgical means. Asintering process for cermets and/or the cermet-containing bearingelement proceeds just like with homogeneous powders with the exceptionthat the metal is compacted more strongly at the same pressuring forceas compared to the ceramic material. The cermet-containing bearingelement has a higher thermal shock and oxidation resistance thansintered hard metals. In most cases, the ceramic components of thecermet are aluminum oxide (Al₂O₃) and zirconium dioxide (ZrO₂), whereasniobium, molybdenum, titanium, cobalt, zirconium, chromium areconceivable as metallic components.

In the context of one embodiment, the term, “comprising a cermet”,refers to a mixture of materials in which a part of the material of theconduction element or other element is connected to a cermet.Accordingly, this is understood to mean that the corresponding elementis cermet-containing. It can be formed and fired from acermet-containing material and/or powder. This scope also encompasses adevelopment, in which the element consists of a cermet. In this variant,the corresponding element—such as conduction element or the holdingelement to be illustrated below—are completely made of a cermet.

In order to integrate the electrical bushing into the housing of acardiac pacemaker, the electrical bushing includes a holding element.Said holding element is arranged in annulus-like manner around theinsulation element. The holding element serves for connection to thehousing in a non-positive or positive-type fit. For this purpose, amedia-tight connection must arise between the holding element and thehousing. In one development, the electrical bushing includes a holdingelement that includes a cermet. The cermet-containing holding elementcan be connected to the housing of the implantable medical device in asimple, long-lasting, and hermetically sealing manner.

A further embodiment has the holding element not comprise a cermet, butconsist of a cermet. Moreover, it is conceivable that the conductionelement and the holding element are made of the same material. In thisvariant, the same materials are used for the conduction element and theholding element. In one embodiment, this concerns a resistant,conductive, and biocompatible cermet. Since both the holding element andthe conduction element are still to be connected to metallic components,both must include the corresponding prerequisites for welding orsoldering. If a cermet is found that meets the specified prerequisites,it can be utilized for both the holding element and for the conductionelement in order to thus obtain a particularly inexpensive electricalbushing.

One embodiment includes an insulation element that is made from aninsulating composition of materials. The insulation element serves toinsulate the conducting wire from the holding element and any otherobjects of the implantable medical device. Electrical signals proceedingthrough the conducting wire are not to be attenuated or short-circuitedby contacting the housing of the implantable device. Moreover, theinsulation element must include a biocompatible composition in order tobe implanted medically. For this reason, it is preferred in oneembodiment for the insulation element to consist of a glass-ceramic orglass-like material. It has proven to be preferred in one embodiment forthe insulating composition of materials of the insulation element to beat least one from the group of aluminum oxide (Al₂O₃), magnesium oxide(MgO), zirconium oxide (ZrO₂), aluminum-titanate (Al₂TiO₅), andpiezo-ceramics. The aluminum oxide ceramic material has a highelectrical resistance and low dielectric losses. Moreover, theseproperties are supplemented by the high thermal resistance as well asgood biocompatibility.

Another development of the bushing according to one embodiment ischaracterized in that the holding element includes at least one flange,whereby, in particular, the flange is conductive like a metal. Theflange serves to seal the electrical bushing with respect to a housingof the implantable device. The holding element holds the electricalbushing in the implantable device. In the development described atpresent, the holding element includes at least one flange on oneexternal surface. Said flanges form a bearing, which can be engaged bythe lids of the implantable medical device, in one embodiment can beengaged in a sealing manner. Accordingly, the holding element withflanges attached to it can have a U- or H-shaped cross-section.Integrating at least one flange into the holding element ensures safe,impact-proof, and long-lasting integration of the electrical bushinginto the implantable device. In addition, the flanges can be designedsuch that the lids of the implantable device are connected clip-like tothe holding element in a non-positive fit- and/or positive fit-likemanner.

Another development of the electrical bushing according to oneembodiment is characterized in that the at least one flange includes acermet. In the scope of this development, both the holding element andthe flange include a cermet. In one embodiment, flange and holdingelement are made of the same material. Designing the flange as cermetallows it to be sintered easily and inexpensively as part of the holdingelement and jointly with the insulation element and the conductionelement in the scope of the method to be described below.

One embodiment uses at least one cermet-containing conduction element inan electrical bushing for an implantable medical device. In thiscontext, any features and details that were described in relation to theelectrical bushing and/or the method shall also apply in relation to theuse of a cermet-containing bearing element.

Another embodiment is an implantable medical device, for example, acardiac pacemaker or defibrillator, having an electrical bushingaccording to any one of the embodiments described above. In thiscontext, any features and details that were described in relation to theelectrical bushing and/or the method shall also apply in relation to theimplantable medical device.

One embodiment also relates to a method for producing an electricalbushing for an implantable medical device. Some disadvantages arisingduring the production of electrical bushings have been described above.The objective resulting therefrom has also been specified above.According to one embodiment, the method for producing an electricalbushing for an implantable medical device includes the following steps:

-   -   a. generating an insulation element green compact for an        insulation element from an insulating composition of materials;    -   b. forming at least one cermet-containing conduction element        green compact for a conduction element;    -   c. introducing the at least one conduction element green compact        into the insulation element green compact;    -   d. firing the insulation element green compact and the at least        one conduction element green compact to obtain an insulation        element with at least one conduction element.

Any features and details that are described in this context in relationto the electrical bushing shall also apply in relation to the methodaccording to the embodiment, and vice versa.

One special feature of the method according to one embodiment resultsfrom both the insulation element and the conduction element comprisingceramic components which are processed by means of a sinteringprocedure. According to procedural step a), an insulation element greencompact is formed from an insulating composition of materials. This canbe effected by pressing together the composition of materials in a mold.For this purpose, the insulating composition of materials is a powdermass whose powder particles illustrate at least a minimum of cohesion.This is commonly effected in that a grain size of the powder particlesdoes not exceed 0.5 mm. In this context, the production of a greencompact is effected either by pressing powder masses or by forming andsubsequent drying. Procedural steps of this type are also used to formthe cermet-containing conduction element green compact.

One embodiment provides the powder that is pressed into the conductionelement green compact to be cermet-containing or to consist of a cermet.Subsequently, the two green compacts—the insulation element greencompact and the conduction element green compact—are placed together.After this step, called step c), the two green compact are fired—whichis also called sintering. In the process, the green compacts aresubjected to a heat treatment below the melting temperature of thepowder particles of the green compact. In the process, the porosity andthe volume of the green compacts are decreased markedly. Accordingly, aspecial feature of the embodiment is that the insulation element and theconduction element are fired jointly. There is no subsequent need forconnection of the two elements any more. The firing process effectsconnection of the conduction element to the insulation element that isof the non-positive fit- and/or positive fit- and/orsubstance-to-substance-type. Thus, hermetically sealed integration ofthe conduction element into the insulation element is achieved. There isno need for subsequent soldering or welding of the conduction element inthe insulation element. Rather, the joint firing and the use of acermet-containing green compact effects a hermetically sealed connectionbetween the insulation element and the conduction element.

One development of the method according to one embodiment ischaracterized in that step a) includes a partial sintering of theinsulation element green compact. As part of said only partialsintering, the green compact of the insulation element is heat treated.This is already associated with some shrinkage of the volume of theinsulation element green compact. But the volume of the green compactdoes not reach its final stage. Rather, another heat treatment as partof step d) is required, in which the insulation element green compactand the conduction element green compact are shrunk to their final size.In said development, the green compact is heat treated only partly inorder to already attain a certain surface hardness to render thehandling of the green compact of the insulation element easier. This isexpedient, for example, in the case of insulating compositions ofmaterials which can be pressed into the form of a green compact onlywith some difficulty.

Another development is characterized in that the conduction elementgreen compact is also already partly sintered in step b). As describedabove for the insulation element green compact, the conduction elementgreen compact can also be sintered to some extent in order to alreadyattain a certain surface stability. It needs to be noted in this contextthat the final, complete sintering in this development also does notoccur until step d). Consequently, the conduction element green compactalso attains its final size only in step d).

Another development of the method is characterized in that the methodincludes the following steps preceding step d):

-   -   producing a cermet-containing holding element green compact for        a holding element;    -   introducing the at least one bearing element green compact into        the insulation element green compact, and introducing the        insulation element green compact into the holding element green        compact;    -   whereby step d) includes:    -   d. firing the insulation element green compact and the at least        one bearing element green compact and the holding element green        compact to obtain an insulation element with at least one        bearing element and a holding element.

The special feature of this procedural step is that, aside from thebearing element green compact and the insulation element green compact,the bearing element green compact is also sintered in one step. Allthree green compacts are generated, then joined, and subsequently firedand/or sintered as a unit. In one development, the production of the atleast one cermet-containing holding element green compact can includepartial sintering. In this context, the fringe green compact is againprovided to be partly sintered in order to attain higher surfacestability.

FIG. 1 illustrates, in an exemplary fashion, an implantable device 100,such as, for example, a cardiac pacemaker, with an electrical bushing 10being integrated into the metallic housing thereof. The electricalbushing 10 is connected to the housing 110 of the implantable device 100in a hermetically sealed manner, for example, by means of welding. Inone example, it is therefore advantageous for a holding element 20 ofthe electrical bushing 10 to include a metal that can be welded to thehousing 110 both easily and reliably. The electrical bushing 10 servesto establish an electrical connection between the hermetically sealedinterior of the medical device 100 and the exterior.

Accordingly, a conducting coil 120, which is indicated onlyschematically herein and is connected to an stimulation electrode, canbe attached to the electrical bushing 10. Stimulation electrodes of thistype are used, for example, in heart muscles in order to allow signalsof the cardiac pacemaker to be conducted to the muscle. In order toattain hermetic sealing, the conducting wire 30 is embedded into aninsulation element 40. The insulation element 40 leads to the formationof a hermetic seal between the holding element 20 and the at least oneconducting wire 30 in a through-opening 22 that is formed by theannulus-like holding element 20. The electrically insulating insulationelement prevents short-circuiting between the electrically conductiveelongated conducting wire 30 and the metallic housing 110 and/or themetallic holding element 20.

In electrical bushings according to the prior art, a metallic wire isused as conduction element and needs to be soldered into an insulationelement. For this purpose, the insulation element includes acylinder-like bushing for the conduction element, with said bushingbeing provided with a metallic coating on its internal wall. Solderinghas proven to be error-prone and expensive. FIG. 2 illustrates anelectrical bushing 10 according to one embodiment that overcomes thedisadvantages mentioned above.

In one embodiment, the electrical bushing 10 includes an annulus-likeholding element 20. The holding element 20 serves to hold the electricalbushing 10 in the implantable medical device 100. The holding element20, designed to be annulus-like, includes a through-opening 22. This isparticularly evident from FIG. 3, which illustrates a top view onto theelectrical bushing 10 illustrated in a section in FIG. 2. Designedrectangular in shape and annulus-like, the holding element 20 possesses,on its interior, the through-opening 22, which is designed to berectangular in the present case. At least one elongated conductionelement 30 extends through said through-opening 22. In the exemplaryembodiment illustrated, a total of six conduction elements 30 extendthrough the holding element 20. An insulation element 40 is arranged inthe through-opening 22 such that hermetic sealing is effected betweenthe holding element 20 and the conduction element 30. The specialfeature, according to one embodiment, of the electrical bushing 10illustrated results from the conduction element 30 comprising a cermetor consisting of a cermet.

A cermet is a composite material made of ceramic materials in a metallicmatrix. The special feature of a cermet-containing conduction element 30of this type is that it can be sintered in a single procedural stepjointly with the also ceramic-containing insulation element 40. Thus, noundesirable through-openings, fissures or imperfections arise betweenconduction element 30 and insulation element 40 anymore. Rather, amedia-tight connection is created between the two elements 40, 30. Theindividual procedural steps for producing an electrical bushing 10according to one embodiment, are as follows:

-   -   a. generating an insulation element green compact for an        insulation element (40) from an insulating composition of        materials;    -   b. forming at least one cermet-containing conduction element        green compact for a conduction element (30);    -   c. introducing the at least one conduction element green compact        into the insulation element green compact;    -   d. firing the insulation element green compact and the at least        one conduction element green compact to obtain an insulation        element (40) with at least one conduction element (30).

The special feature of the method according to the embodiment resultsfrom both the insulation element green compact and the conductionelement green compact, each being pressed from powders and subsequentlybeing fired. It is therefore feasible in few procedural steps togenerate a green compact that include both the conduction element greencompact and the insulation element green compact and subsequently firesaid total green compact. In one development, not only the insulationelement 40 and the conduction element 30, but also the holding element20, are pressed from powders and sintered.

Accordingly, the holding element 20 is also produced from acermet-containing powder in one production step. Subsequently, the threegreen compacts—holding element 20, conduction element 30, insulationelement 40—are placed together. This results in the electrical bushing10 in a green compact stage. Subsequently, the three green compacts arefired jointly. The electrical bushing 10 resulting therefrom, on the onehand, meets all requisite electrical requirements and, on the otherhand, is produced in one step with no need for subsequent soldering orwelding of individual elements. Moreover, the metal-containing, acermet-comprising holding element 20 facilitates simple, long-lastingconnection to the housing of the implantable medical device 100.

FIG. 4 again illustrates the individual components of the electricalbushing 10, in magnification. This is a detail magnification of theregion of FIG. 3 denoted I. Made from an electrically insulatingcomposition of materials, the insulation element 40 surrounds theconduction element 30. For example, conducting coils for a cardiacpacemaker can be attached to said conduction element 30. The insulationelement 40 is surrounded by a holding element 20 that is designed to beannulus-like. Said holding element 20 is cermet-containing in thedevelopment illustrated.

The holding element 20 can include a flange for integration of theelectrical bushing 10 in the implantable medical device 100. A flange isnot shown in the figures. A housing 110 of the device 100 can touchagainst the flange in order to thus facilitate a hermetically sealedconnection between both elements. In one embodiment, the holding element20 and the flange are made of the same material and/or in the form of asingle part.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method for producing an electrical bushing foran implantable medical device, the method comprising: generating aninsulation element green compact for an insulation element from aninsulating composition of materials; partially sintering the insulationelement green compact; forming at least one cermet-containing conductionelement green compact for a conduction element; introducing the at leastone conduction element green compact into the insulation element greencompact; firing the insulation element green compact and the at leastone conduction element green compact to obtain an insulation elementwith at least one conduction element; characterized in that partiallysintering the insulation element green compact forms a surface hardnessof the insulation element green compact thereby allowing for handlingthe insulation green compact before the firing of the insulation elementgreen compact and the at least one conduction element green compact. 2.The method according to claim 1, further comprising surrounding theinsulation element with a holding element.
 3. The method according toclaim 1, characterized in that forming at least one cermet-containingconduction element green compact comprises partial sintering of theconduction element green compact.
 4. A method for producing anelectrical bushing for an implantable medical device, the methodcomprising: generating an insulation element green compact for aninsulation element from an insulating composition of materials;partially sintering the insulation element green compact; forming atleast one cermet-containing conduction element green compact for aconduction element; introducing the at least one conduction elementgreen compact into the insulation element green compact; firing theinsulation element green compact and the at least one conduction elementgreen compact to obtain an insulation element with at least oneconduction element, characterized in that, prior to firing theinsulation element green compact and the at least one conduction elementgreen compact, the method comprises: producing a cermet-containingholding element green compact for a holding element, introducing atleast one bearing element green compact into the insulation elementgreen compact, and introducing the insulation element green compact intothe holding element green compact; whereby firing the insulation elementgreen compact and the at least one conduction element green compactcomprises firing the insulation element green compact and the at leastone bearing element green compact and the holding element green compactto obtain an insulation element with at least one bearing element and aholding element.
 5. The method according to claim 4, characterized inthat the production of the cermet-containing holding element greencompact comprises partial sintering.
 6. A method for producing anelectrical bushing for an implantable medical device, the methodcomprising: generating an insulation element green compact for aninsulation element from an insulating composition of materials; formingat least one cermet-containing conduction element green compact for aconduction element; partially sintering the at least onecermet-containing conduction element green compact; introducing the atleast one conduction element green compact into the insulation elementgreen compact; producing a cermet-containing holding element greencompact for a holding element; introducing the insulation element greencompact into the holding element green compact; firing the holdingelement green compact, the insulation element green compact and the atleast one conduction element green compact to obtain an insulationelement with at least one conduction element and a holding element.